Nucleation of ice affects the properties of clouds and the formation ofprecipitation. Quantitative data on how ice nucleating particles (INPs)determine the distribution, occurrence and intensity of precipitation arestill scarce. INPs active at −8 °C (INPs) were observed for2 years in precipitation samples at the High-Altitude Research StationJungfraujoch (Switzerland) at 3580 m a.s.l. Several environmentalparameters were scanned for their capability to predict the observedabundance and variability of INPs. Those singularly presenting thebest correlations with observed number of INPs (residual fraction ofwater vapour, wind speed, air temperature, number of particles with diameterlarger than 0.5 µm, season, and source region of particles) wereimplemented as potential predictor variables in statistical multiple linearregression models. These models were calibrated with 84 precipitation samplescollected during the first year of observations; their predictive power wassuccessively validated on the set of 15 precipitation samples collectedduring the second year. The model performing best in calibration andvalidation explains more than 75 % of the whole variability ofINPs in precipitation and indicates that a high abundance ofINPs is to be expected whenever high wind speed coincides with airmasses having experienced little or no precipitation prior to sampling. Suchconditions occur during frontal passages, often accompanied by precipitation.Therefore, the circumstances when INPs could be sufficiently abundantto initiate the ice phase in clouds may frequently coincide withmeteorological conditions favourable to the onset of precipitation events.
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